Many engines incorporate an air filter to clean the air stream that passes into the engine. These filters are commonly secured on structures that are physically proximate to the engine; for example, on the frame to which the engine is secured, to a nearby fire wall, or even to the engine itself. They are generally secured in a manner that allows them to be periodically removed and the filtering elements renewed. The filter generally includes an external housing and internal filter elements.
In one type of arrangement, the housing is secured to the surrounding structure by a mounting-band assembly, which is itself rigidly attached to the surrounding structure. Such band assemblies are very often constructed of metal, for reasons of durability, ease of fabrication, adequate mechanical properties, and so on. The mounting-band assemblies incorporate a discontinuous band that surrounds, and maintains an interference fit with, the periphery of the filter housing. Typically, the ends of the band have been secured by mechanisms such as an over-center clamp, or a bolt running between an ear on each end of the band.
In the past, such mounting-band assemblies have functioned to hold filter housings in place when the housing was constructed of metal. More recently, however, manufacturers have begun to construct filter housings out of was constructed of metal. More recently, however, manufacturers have begun to construct filter housings out of other materials, such as polymers. When such polymer housings are secured by the filter mounting-band assemblies that have heretofore been commonly used, the housings exhibit, over time, a narrowing, or pinched-in "waist," underneath the band.
The creation of this waist can progress to a point where the band assembly can no longer hold the housing firmly in place. Consequently, the housing rattles loose when the engine is operated, thereby bringing the service life of the housing to a premature end. Moreover, the uncontrolled motion of the now-loose filter with the band assembly is an usual operating mode, which subjects the band assembly to undesigned-for stresses. This, in turn, can result in the band assembly also failing prematurely.
One of the goals of the present invention is to solve this problem of securing polymer filter housings with metal mounting-band assemblies.
Engines are often subjected to substantial heat when in operation. For example, the engine itself generates a significant amount of heat when in operation, and then gradually cools when turned off. The engines also are often operated in ambient conditions that are quite hot. As a consequence, over periods of use the proximately-located mounting-band assembly and filter housing will also be subjected to heating and cooling.
These heating cycles apparently did not pose a great problem when both the band assembly and housing were made of metals with similar thermal expansion rates. In such an arrangement, as the housing enlarged during heating, the band assembly would also enlarge to approximately the same extent. Consequently, the forces between band assembly and housing apparently would stay within acceptable limits.
The polymer materials now being used in filter housings, however, have properties that are different from the previous metal materials. In particular, the polymer materials have a different, greater thermal expansion rate than the previous metal materials. Thus, as a polymer housing and metal mounting-band assembly are heated during the operation of the engine, the housing will expand significantly more than the metal of the band. This will greatly increase the forces between the filter housing and an ordinary mounting-band assembly.
The polymer materials also have a tendency to cold flow. Thus, when a polymer housing is heated and then pressed by a more slowly-expanding, non-adjusting band assembly, the housing will deform by expanding more in those regions where it is not constrained by the band. When the filter housing cools, the polymer will retain at least part of this deformed shape. As the filter housing undergoes repeated heated and cooling cycles, it will continually deform further, to the point where it can no longer be securely retained by the band.